FEEDING TIMES 
173 
are unusual, and that it is impracticable to keep the mouse in such a constrained position for 
very long so chiggers with unusually long feeding times are not recorded. 
For the wild mites records are kept on punch-cards, one for each rat (or occasion, for 
mark-release rats) showing the species of rat, the species of mite recovered, the register number 
of the rat, date and locality trapped, and its exposure to infestation (e.g., one-day, two-day, 
unknown). For each day after capture of the rat is shown the number of mites recovered, by 
species. Normal procedure would be for a rat to be trapped during the night. The trap 
with its encaged rat would be brought to the laboratory during the morning and set up in a 
cage over a water tray at sometime between 9 a.m. and mid-day. The tray would then be 
examined daily between 9 a.m. and 11 a.m. The “ day” for which a mite is recorded as 
detaching is thus a 24 hour period from about 10 a.m. to 10 a.m., with zero on the morning 
after the rat was trapped. 
Interpretation of results 
For laboratory bred chiggers, put onto a mouse at a known time, results are straight- 
forward. The validity of applying them to field conditions however is doubtful, for several 
reasons. The chiggers are put onto the head of a mouse during the day, whereas in nature they 
would climb onto some lower part of the body probably during the night and make their way 
to the ears. Again, although mice are convenient laboratory animals for studying infections 
transmitted by the chiggers, they are not readily acceptable as hosts for the mites (Cockings 1948, 
Harrison and Audy, 1951) a factor which may or may not affect the feeding time. 
Mark-recapture experiments 
Marked rats are normally released at the point of capture when the traps are visited in the 
morning but sometimes they are released in the evening. Rats are nocturnal, and in our 
experience mites are active only when the dew is on the ground, that is to say that they will 
have gone into hiding by 9 a.m. and will not become active until after sunset. Whether the 
rat is released in the morning or in the evening, therefore, it is unlikely to pick up any mites 
before sunset (about 7 p.m.). The rats are likely to be trapped in the earlier part of the night 
after which their chances of picking up mites are considerably reduced judging from the results 
of setting out rats in cages as bait. It seems fair, therefore, to allow that a chigger on a rat 
trapped within 24 hours of release has been picked up during the first half of the night, say 
between 7 p.m. and 1 a.m., central time 10 p.m. 
If the recaptured rat is set over water at about 10 a.m. the next morning, the first day for 
mite recovery will extend from 10 a.m. on day zero to 10 a.m. on day one, with a central time 
of 10 p.m. Mites found in the tray on day 1 may, therefore, fairly be counted as having fed 
for a period grouped about one day, and the best estimate of the mean feeding time will be 
obtained by treating the numbers recovered on days 1,2,3, etc., as the numbers feeding for 
periods of central values 1,2,3, etc., days. 
In fact it appears that most of the chiggers leave the rat during the night or early morning. 
Table 1 shows the result of examining trays at 8 a.m., 12 noon, and 4 p.m., for the two mites 
T. akamushi and T. deliensis on two host species. The total number of mites recovered at 
each of these times is shown compared with the number “ expected ” if the mites came off 
irrespective of time. The 8 a.m. count represents a sixteen hour collecting period, and the 
12 noon and 4 p.m. counts represent four-hour periods each, and therefore the numbers would 
be expected to be in the rado of 4: 1 : 1. In fact there is a great excess of mites in the 8 a.m. 
count, showing that most mites must detach during the night or early morning. The fact 
that the 12 noon count is consistently greater than the 4 p.m. count suggests either that the 
mites may spend some time wandering about on their host before dropping off, or that the 
modal time of detachment is in the morning, nearer to 8 a.m. than 4 p.m. 
MALAYA , No. 26, 1953 
